An electrical or power substation involves electricity transmission and distribution systems where voltage is transformed from high to low or the reverse using transformers. Electric power may flow through several substations between generating plant and consumer, and in the process be transformed through many voltage levels in several steps.
Appropriate equipments are selected for these functions depending on whether the substation is a transmission, sub-transmission or distribution substation. These equipments could include transformers, reactors, capacitor banks, circuit breakers, disconnector switches etcetera. Substation Automation can involve protection, control, monitoring and metering functions of the above mentioned equipment and derives reliable information for efficient functioning of the substation. Currently different types of Intelligent Electronic Devices (IEDs) are used in a Substation Automation (SA) system to cater to protection, control, monitoring and metering functions of different substation equipment. The IEDs are microprocessor-based controllers of power system equipment, such as circuit breakers, transformers, and capacitor banks. For example, the IEDs receive data from sensors and power equipment, and can issue control commands, such as tripping circuit breakers if they sense voltage, current, or frequency anomalies, or raise/lower voltage levels in order to maintain the desired level. Known types of IEDs include protective relaying devices, load tap changer controllers, circuit breaker controllers, capacitor bank switches, recloser controllers, voltage regulators, etc. These IEDs can be advantageous because, with the available microprocessor technology a single unit can perform several protection, metering, monitoring and control functions concurrently.
Substation Automation can be an important and complex aspect for maintenance and control of different equipments involved in different processes within the substation. For this purpose the substation communication network can be categorized into three layers such as process bus, bay bus, station bus. Equipments like the transformers, Merging Unit, circuit breakers, isolators and switches reside in the substation switch yard. These devices are connected through the process bus where the control commands, digitized voltage/current information, etc, flow across various layers of the substation communication architecture. The secondary devices are the intelligent electronic devices performing the protection, control, metering and monitoring functionalities by communicating with the primary equipments and hosted by the bay bus. The station bus connects the operator workstation, engineering workstation, etc, of the substation automation system to the rest of the substation elements, which communicate over the process and bay bus.
The IEDs in various layers of the substation communication network can use different communication profiles for communicating their data. Multiple protocols exist for Substation Automation, which include many proprietary protocols with custom communication links. However, interoperation of devices from different vendors can be highly desired for simplicity in implementation and use of Substation Automation devices.
The IEC61850 standard from International Electrotechnical Commission (IEC) is a standard for communication networks and systems in substation, which advocates interoperability amongst Intelligent Electronic Devices (IEDs) from various manufacturers using common engineering models, data formats and communication protocol. Recent IEDs are designed to support the IEC61850 standard for substation automation by implementing the IEC61850 profiles as per the application requirements, thereby providing interoperability and advanced communications capabilities and these IEDs are termed as IEC61850 compliant IEDs. Hereinafter the term IED should be interpreted as IEC61850 compliant IED unless specified otherwise.
The IEC 61850 standard promotes the Merging Unit (MU) which provides the standard digital interface to both conventional and non-conventional instrument transformers. The MU communicates the digitized voltage/current information using the IEC 61850-9-2 profile across the substation communication network. The IEDs in the bay performs its function by utilizing the IEC 61850-9-2 data from MU and coordinating with the other IEDs in the substation automation system. Such communications between IEDs involve the status update, executing commands based on the status of IED group, etc., and are based on the GOOSE (Generic Object Oriented Substation Event) message format defined by the IEC 61850. The substation operator can monitor and control the substation automation system from their operator workstation terminal by communicating with the IEDs in the communication network through the MMS (Manufactures Message Specifications) profile. Since the operator workstation and/or the engineering workstation are located in the control center which is a central point receiving the information from multiple bays, data acquisition from various IEDs are session based, and monitoring is less time critical, the TCP/IP based MMS profile can be preferred in such conditions.
The MMS stack is a heavy weight stack as it supports various control blocks like report, log, etc., and the MMS traffic along with the sampled measured value traffic in the process bus would cause system reliability issues. Moreover the MMS clients can obtain desired information of the system from the bay level IEDs supporting MMS stack for supervisory and control purpose, which encourages implementation using the GOOSE profile rather than the MMS stack in process bus IEDs. It is to be noted that many standard features in IEC 61850 are defined and supported for IEDs communicating over the bay bus and not much for applications over the process bus.
Exemplary embodiments as described herein can enable and coordinate mission or/and time critical functions for the IEDs that communicate using GOOSE messages over the process bus.